0.012" is very small. You have a small shot at filling it with underfill epoxy--Loctite Hysol makes some good ones, but you will need to heat the assembly up and evacuate. Even then the epoxy might have trouble running down there. Whether to bother trying depends on the operational use--Even though epoxy won't flow down there, somehow corrosives might. I think as long as you cap it off good it'll be fine for most uses. Smallest hole I've filled, even with heated underfill (but not evacuated) was 0.06" deep with a 0.025" diameter. It was not fun to fill, but I could not get the assembly into a vacuum chamber.
Wayne Thayer
________________________________
From: TechNet on behalf of Whittaker, Dewey (EHCOE)
Sent: Wed 8/15/2007 5:20 PM
To: [log in to unmask]
Subject: Re: [TN] Drill Rework
I don't mean to sound holier than thou, but I don't like partial depth
drilling to cut traces and I don't advise filling a whole that is not
the sum of its parts. If this part went into John Burke's Refrigerator,
no one would care because the English like warm Beer anyway. However, if
there is integrity required or long term reliability, I would do
additional testing/cleaning of the hole before I applied a well
engineered epoxy with a structured process. Things to consider are as
follows:
* Verify TCE compliancy with FR4 substrate
* Verify ability to seal to prevent moisture/contamination
ingression
* Verify the by-products of the cure are not a potential
contaminant
* Verify the by-products of the cure are not potentially
corrosive
* Verify the by-products of the cure are not a growth medium
* Verify the by-products of the cure are not conducive to
forming an electrical migration path
* Verify bullets 3 through 6 are still acceptable in the
presence of humidity and a DC bias voltage
* Verify that the adhesive and it's by-products do no outgas
* Verify there are no amines in the formulation
* Verify that the adhesive does not create any occupational
hazards
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tony Steinke
Sent: Wednesday, August 15, 2007 2:28 PM
To: [log in to unmask]
Subject: Re: [TN] Drill Rework
Kerry,
A two part epoxy by 3M followed up with a 200F bake to fully cure should
be
fine.
Tony Steinke
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kerry McMullen
Sent: Wednesday, August 15, 2007 2:28 PM
To: [log in to unmask]
Subject: [TN] Drill Rework
Hi,
I have a .062 FR406 board where I need to drill out a trace that is
causing a problem. The trace is .020" down in the board (Layer 4).
The
drill size is .012.
After I have drilled out (opened) the trace, what do you suggest I fill
the drill hole with?
We have done the rework, and it works fine. I am just curious as to if
I
should fill the hole with epoxy.
Thanks in advance,
Kerry
Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
825 University Avenue
Norwood, MA 02062-2643
(T) 781-467-5468
(C) 508-631-1832
(F) 781-461-0993
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